This application relates generally to scanned-spot-array lithography systems, and more specifically to scanned-spot-array lithography systems using deep ultraviolet (DUV) sources.
Scanned-Spot-Array Optical Lithography is a maskless lithographic printing method in which an array of diffraction-limited focused-radiation spots is raster-scanned over a printing surface (a photosensitive optical recording medium) to synthesize a high-resolution recorded image. The spots may be individually modulated by a spatial light modulator, or they may be collectively modulated by a single modulator.
A scanned-spot system described in U.S. Pat. No. 5,900,637 (the '637 patent) comprises Fresnel zone plates 200, which convert parallel (i.e., collimated) beamlets 212 of electromagnetic radiation into focused beamlets 213 converging to foci 215 on a printing substrate (the '637 patent's FIG. 2; col. 2, line 55 to col. 3, line 8; and col. 4, lines 4-27). The beamlets are individually modulated by micromechanical shutters 219 between the zone plates and the substrate. Alternatively, the beamlets may be modulated by means of either shutters or micromechanical mirrors preceding the zone plates in the parallel beam paths (the '637 patent's FIG. 3; col. 4, lines 23-44).
An alternative spot-scanning system disclosed in U.S. Pat. No. 6,133,986 (the '986 patent) similarly uses an array 11 of light-modulating elements such as micromirrors to modulate individual beamlets, which are focused by a microlens array 2 onto foci on a printing surface 12. (See the '986 patent's FIG. 2 and col. 4, lines 28-48). In an improvement over the '637 patent the beamlets all pass through a common projection aperture 7 of a projection system 1, which images the modulator elements onto corresponding microlenses. (By contrast, the '637 patent's FIG. 3 illustrates the beamlet light paths as being parallel and non-intersecting in the space between the mirror array and the zone plates.) The focusing elements in the '986 patent may be continuous-profile microlenses, which have higher optical efficiency and less chromatic aberration than zone plates. Other possible microlens forms include micro-Fresnel lenses or binary optics (the '986 patent's col. 13, lines 34-38). The '986 patent also describes methods for sensing and correcting positional errors between the microlenses and the printing surface, e.g., by means of a piezoelectric transducer coupled directly to the microlens array (col. 19, line 19 to col. 25, line 9).
U.S. Pat. No. 6,897,941 (the '941 patent) discloses a spot-scanning system, which is similar to those of the '637 and '986 patents in that it uses a spatial light modulator to modulate an array of parallel optical beams, and focuses the modulated beams onto a spot array by means of microlens focusing elements. (See the '941 patent's col. 4, line 60 to col. 5, line 15 and col. 6, lines 24-40.) As illustrated in the '941 patent's FIGS. 1 and 2, the modulated beams 106 are parallel in the sense of being collimated between the collimating optics 103 and focusing elements 114. The beamlets may be focused directly onto the printing substrate 120 in the manner of the '637 and '986 patents' inventions, or the focused spots may be imaged through a demagnifying lens 150 (col. 6, lines 53-55). Positioning errors may be controlled by means of a compensator system similar to the '986 patent's positioning feedback and control mechanisms (the '941 patent's col. 3, lines 62-65 and col. 11, line 66 to col. 12, line 21). In an improvement over the '637 and '986 patents, the system resolution is improved by incorporating a “beam shaper” (or “apodizer”) comprising an array of shaped apertures in the parallel beam path (col. 2, lines 50-55; col. 3, lines 26-38; col. 5, lines 34-64). (the '986 patent discloses a different apodization technique in which the apodization is applied to the projection aperture, not to an “array of shaped apertures”; see the '986 patent's col. 11, lines 15-20.)